1. Field of the Invention
The present invention relates to polyethylene compositions and films thereof combining excellent optical and mechanical properties with good processability and downgauging possibilities while assuring an excellent stiffness. This polyethylene composition can therefore be used for film applications, requiring this unique combination of properties, such as but not exclusively, food or non-food packaging, personal care products, agricultural or industrial products.
2. Description of the Prior Art
Low density polyethylene (LDPE) offers excellent optical properties and can be processed at low temperatures and pressures while maintaining a good melt strength. LDPE has however limited possibilities for downgauging, due to a low draw ratio, and a low stiffness.
Linear-low-density polyethylene (LLDPE) has greatly improved downgauging possibilities and excellent tear and impact properties; its stiffness however remains low and its processability is well below that of LDPE. Also, conventional LLDPE's optical properties do not match those of LDPE. Optical properties of LLDPE have been improved by using metallocene-catalyzed LLDPE (mLLDPE) resins; stiffness is however not improved in these products and the processability of these grades is generally worse than that of conventional LLDPE.
Wherever high rigidity is needed, LDPE and LLDPE compositions will require overly thick structures. Especially for LLDPE, where excellent impact and tear properties render its downgauging capability useful, the lack of rigidity may be a main drawback. High rigidity may be a requirement for the end product, it is very often a necessity for product handling.
Conventional medium density polyethylene (MDPE) offers a much improved rigidity, excellent processability and downgauging possibilities. MDPE however lacks the good optical properties of LDPE or LLDPE.
Blends of conventional MDPE with LDPE and/or LLDPE can be used for improving rigidity and/or downgauging and/or processability of LDPE and/or LLDPE but do not provide their good optical properties. WO 95/27005 discloses mixtures of LDPE with LLDPE or mLLDPE. The stiffness of their resins is insufficient.